The present invention relates to a reflow furnace for heating a carried circuit module to perform reflow soldering.
Hitherto, there is adopted a method of soldering that for example, when a circuit module is assembled onto a mother board, the circuit module, in which a soldering bump (for example, 95Pb5Sn soldering and the like) is placed on a soldering portion, is disposed on the mother board, and the mother board, on which the circuit module is disposed thus, is carried into a reflow furnace which is filled with nitrogen and is maintained a temperature 500xc2x0 C. or more so that a reflow soldering is performed. In this case, it often happens that there is provided such an arrangement that the mother board and the circuit module on the mother board are conveyed by a conveyance belt into a reflow furnace and are carried out from the reflow furnace as they are on the conveyance belt. In such a case, it is needed for the reflow furnace to have a carrying inlet for carrying the circuit module and the like into the reflow furnace and a carrying outlet for carrying the circuit module and the like out. In the middle of reflow soldering, exposure to oxygen makes it easy to bring about oxidation. This involves a degradation of reliability in mounting. Accordingly, in order that oxygen is hard to enter inside of the reflow furnace, height of apertures of the carrying inlet and the carrying outlet is limited to the order of 1 cm to 2 cm or so which permits a circuit module mounted with no fin to barely pass through the apertures.
On the contrary, recently, in order to increase the productivity, there is increased such a demand that an extremely high circuit module is carried into a reflow furnace to perform a reflow soldering in such a way that the assembled circuit module, on which a heat sink fin is already mounted, is mounted on a mother board. To carry the circuit module, on which a heat sink fin is mounted, into the reflow furnace and carry out the same, there is needed carrying inlet and carrying outlet of the aperture height of 5 cm to 10 cm or so. In this case, simply enlarging the aperture makes air (oxygen in air) easy to enter inside the reflow furnace owing to diffusion or the like. This involves a possibility of degradation of reliability in mounting.
This problem will be described in conjunction with drawings.
FIG. 10 is a typical illustration of a reflow furnace.
FIG. 10 shows a state that a circuit module 101, on which a heat sink fin 102 is already mounted, is put on a mother board 100 through a soldering bump 103. The mother board 100 in this state is put on a conveyance belt 200 travelling in an arrow A direction and is conveyed into a box-like shaped furnace 10.
The box-like shaped furnace 10 comprises a carrying inlet 11 for carrying the mother board 100 (including the circuit modules 101 and the like) into the furnace and a carrying outlet 12 for carrying the mother board 100 out of the furnace.
The furnace 10 has a nitrogen gas supplying section 400 for supplying into the furnace nitrogen gas supplied from a nitrogen gas supplying source 300 via a gas supplying path 301. The nitrogen gas supplying section 400 is provided with a fan 401. The nitrogen gas supplied via the gas supplying path 301 is sent out by the fan 401 into the furnace. The nitrogen gas supplied sent out into the furnace fills the furnace and flows out of the furnace via the carrying inlet 11 and the carrying outlet 12.
Further furnace 10 has a heater 500 in which infrared panel heaters 501 are arranged. The infrared panel heater 501 is a heat source for performing a reflow soldering, and heats the carried mother board 100 (including the circuit modules 101 and the like) to melt the soldering bump 103.
The carrying inlet 11 and the carrying outlet 12 are provided with a fin 111 and a fin 121 on their inside walls, respectively. Those fins 111 and 121 are for preventing oxygen in air from entering from outside of a furnace in some extent.
FIG. 11 is a typical illustration showing a relation between height (H shown in FIG. 10) of an aperture of the carrying inlet or the carrying outlet and a state of entering of the oxygen in air.
FIG. 11(A) shows a case where height H of an aperture is narrow. FIG. 11(B) shows a case where height H of an aperture is wide.
Since oxygen O2 is heavier than Nitrogen N2, oxygen O2 enters a furnace in such a manner that oxygen O2 gets under Nitrogen N2. As compared with a case where height H of an aperture is narrow (FIG. 11(A)), a case where height H of an aperture is wide (FIG. 11(B)) is associated with extremely higher possibility that oxygen O2 enters up to the position nearer to the inside of the main frame of the furnace owing to disturbances of flow of oxygen gas in carrying in and carrying out for the mother board 100 and the like.
As measures of preventing oxygen from entering from the carrying inlet and the carrying outlet, there is considered an adoption of a shutter for selectively covering the carrying inlet and the carrying outlet. In this case, however, when the shutter opens to carry a circuit module into a reflow furnace, air (oxygen) enters the reflow furnace. Thus, there is a need to control a temperature of the reflow furnace in such a manner that a reflow soldering is performed waiting for going down of oxygen density of the reflow furnace. Thus, it takes a lot of time for the reflow soldering and there is a possibility that this will involve a degradation of productivity.
In view of the foregoing, it is an object of the present invention to provide a reflow furnace capable of performing reflow soldering which is high in productivity, while a mounting reliability is maintained high level, even if a height of the aperture of the carrying inlet and the carrying outlet is extensive.
To achieve the above-mentioned object, the present invention provides a first reflow furnace comprising:
a case member having a carrying inlet into which a circuit module is carried and a carrying outlet from which the circuit module is carried out;
a gas supplying section for supplying an inert gas into said case member;
a heating section for heating the circuit module carried into said case member to perform a reflow soldering; and
a nozzle for performing an operation of spraying the inert gas on a soldering portion for the circuit module carried into the case member while said nozzle is moved.
According to the first reflow furnace, there is provided the nozzle as mentioned above. Thus, even if oxygen somewhat enters the furnace from the carrying inlet or the carrying outlet to somewhat increase the oxygen density, so that the oxygen is accumulated on a soldering portion, the accumulated oxygen is blown away by an inert gas ejected from the nozzle so that the reflow soldering is performed in an atmosphere that no oxygen exists. Thus, according to the first reflow furnace; it is possible to implement a high reliability of mounting.
In the first reflow furnace according to the present invention as mentioned above, it is preferable that the first reflow furnace further comprises a sensor for measuring an oxygen density, and said nozzle is selectively operable between emission of the inert gas and stop of the inert gas, and performs said operation when the oxygen density measured by said sensor exceeds a predetermined allowance value.
In this manner, the oxygen density is measured, and the nozzle is operated only in the necessary case in accordance with the measured result. This feature makes it possible to prevent the inert gas from being used to no purpose and also to avoid waste for time necessary for blowing oxygen away.
To achieve the above-mentioned object, the present invention provides a second reflow furnace comprising:
a case member having a carrying inlet into which a circuit module is carried and a carrying outlet from which the circuit module is carried out;
a gas supplying section for supplying an inert gas into said case member;
a heating section for heating the circuit module carried into said case member to perform a reflow soldering; and
fans for sending inert gas inside said case member from the inside of said case member toward the carrying inlet and the carrying outlet, respectively.
According to the second reflow furnace of the present invention as mentioned above, there are provided the above-mentioned fans. This feature makes it possible to avoid mixing of the air (oxygen) from out of the furnace and thereby performing a high reliability of mounting even if an aperture of the carrying inlet and the carrying outlet is large. Here, it is considered that nozzles from which inert gas is jetted via the carrying inlet or the carrying outlet to out of the furnace replace the above-mentioned fans. However, in this case, the inert gas, which is unused in the furnace, is used only for blow off from the carrying inlet or the carrying outlet. This makes it easy to increase an amount of use of inert gas, and thus easy to be a cause of rising the cost of mounting. To the contrary, according to the second reflow furnace of the present invention, the inert gas filled once in the furnace is sent out by the fans. In other words, the inert gas used for removal of oxygen and the like in the furnace is utilized again. Thus, according to the present invention, it is possible to maintain a high reliability of mounting, while suppressing a degree of increment of the total amount of inert gas.
In the second reflow furnace according to the present invention as mentioned above, it is preferable that the second reflow furnace further comprises a sensor for measuring an oxygen density, and each of said fans is selectively operable between air sending of the inert gas and air sending stop of the inert gas, and performs an air sending operation when the oxygen density measured by said sensor exceeds a predetermined allowance value.
Performing air sending only at the necessary time makes it possible to suppress an increment of the amount of use of the inert gas.
In either of the first reflow furnace of the present invention and the second reflow furnace of the present invention, it is preferable that said gas supplying section supplies nitrogen gas as the inert gas into said case member.
As mentioned above, according to the present invention, it is possible to maintain high mounting reliability and high productivity, even if apertures of the carrying inlet and the carrying outlet are large.